Automation error disconnected (80010108), sporadic

I have been working on an excel vba project (for a purchasing department, issuing all sorts of tasks automatically, saved in xlsm format). The project is developing well and I was in my last phase of a beta. One day, I came back from vacation (2nd week of march, may be important) and I was getting a 80010108 error (Automation error, object was disconnected...) I was able to confirm that no change had been done to the spreadsheet. By playing with the spreadsheet further, I found the following:

1) The problem will disappear if I open the VBA editor and save/close the file.
2) After the problem disappeared, reopening the file will allow the vba to run fine, until it is saved/closed again.
3) The problem will persist until the VBA editor is opened again
4) The problem happened all at once on all of my windows XP machines
5) My windows 8 machines seem to be unaffected by the bug. But if the file is in a "broken" state, they will still issue the error message.
6) Going to every previous backup of the xlsm results in the same issue, although the problem did not happen before my vacations
7) No viruses/spywares/rootkits or other were found in any of the computers
8) Putting alerts in every step of the program, and commenting out offending lines when found, allowed me to find that the bug is created by changing (in vba) the captions and values of specific labels and textboxes. It is always the same offending elements, although in the programming, they are part of numerous similar changes
9) Deleting/Copying/Renaming any of the offending lines/elements do not seem to affect the problem... It always occurs on the same elements, independently of its name/position in the programming
10) Saving the xlsm in the older format (xls) prevents the issue from happening again (although I need the extra excel rows and columns). Saving it again in xlsm recreates the same issue.
11) Qualified/Unqualified calls do not seem to change anything (as was suggested by various sites)
12) Reinstalling/Registering/Deleting Registry key for MSComctl.ocx did not change anything (as was suggested by various sites)

I could send the spreadsheet, but I honestly doubt it would be of use since the problem seems related to something else. And the problem occurs on something as simple as : label1.caption="Label Caption"

The problem is literally driving me nuts and seemed to have happened similarly to some other people before... But so far, nothing seemed to have worked for me... Any suggestions?