Corel Draw 12 disappearing line problem

Hi all

I'm running CorelDraw12 but have had at least 1 earlier version. I mainly use it for setting up artwork for making sandblast glass engraving stencils. I appreciate that 12 isn't the latest whizzbangy bells & whistles version, but it does most of what we want.

Got a little problem on which I'd appreciate your comments, plus any help towards clearing it that might be going.

Firstly it's random or, at least, I've not yet worked out what it is that sparks it. It's when I'm doing a particular action, but it doesn't happen every time. It's also fairly rare but just common enough to be both familiar and annoying!

The curious thing is that it has happened on at least 3, possibly 4, different computers. I used to have XP Pro and it happened on that. Now I have Win 8.1 and it keeps happening on that, as well as on another Win 8.1 machine we have. All of those were/are desktop pcs but that last machine was preceded by a Vista laptop. I can't remember for sure, but I think it used to happen on that as well.

To me, all of that points to a program bug rather than an OS thing or relating to a specific machine, but I stand ready to be guided by superior knowledge and/or experience.

OK, the problem.

Most of our artwork is, by comparison, relatively small and simple. Black and white, usually no colour, and just a few lines of text or maybe even a single initial. There may be a logo or other graphic which is usually a vector but could be a bitmap of some sort.

To make sure everything gets lined up straight on the subject piece, I put a set of template lines on the artwork. Firstly, there's a single horizontal line (drawn with the freehand tool but with the grid and forced to horizontal) centred to and 10mm wider than the artwork so it overlaps each side by 5mm. That's set 2mm above the top of the artwork.

Centred and bottom aligned to that horizontal is a 2mm long vertical. Both these lines are ½ point thickness.

I then duplicate these 2 lines, invert them and set them 2mm below the artwork. They should end up as a T and inverted T, centred on the artwork. Dead simple and it works most of the time.

Except that sometimes, when drawing the first horizontal line and I then use the transformation size box to adjust it to that 10mm-wider-than-the-artwork length, the line just disappears! I still see the nodes but the line's not visible and I can't give it any thickness. It happens both with and without the non-proportional box ticked and shows as zero thickness in the toolbar Outline Width box.

Or sometimes, instead of disappearing it becomes a kind of offset, jagged shape visually on-screen, but isn't a "shape" that can be selected in any normal vector graphics manner of speaking.  That "shape" assumes effectively infinite vertical proportions and I get a thick black line/shape shooting to top & bottom of the screen, well beyond the page boundaries.

Up until yesterday it had only ever happened to the horizontal lines, never the short verticals. Yesterday, I had it happen with those as well.

I've got a screenshot that shows one instance of the problem but haven't yet worked out how to post it here ...

I don't particularly want to upgrade but may look to that if I can be reasonably sure it will clear this - and not bring any other glitches.  As I say, it's not every time. Just often enough to be annoying and for me to want to fix it.

Any ideas? Anyone had similar?  Hoping it's not something totally dumb that I've missed ... [*-)]

Hope you can help.