When using Maple 15, sometimes the pagackages and formulas that were previously defined seem to completely drop it.  I'll load packages and assign variables at the beginning of my project, yet after maybe 10 minutes or so, I have to redefine my variables and reload my pacakges.  I have noticed that it happens more often if I try to switch over to the "Text" tab and then back to "Math."  It's very intermittent, Maple will be working just fine churning out graphs,...