Hmm... probably easiest if we look at the crash logs for these. Sync your iPhone with your computer, then go into:
Mac OS X : /Users/(your username)/Library/Logs/CrashReporter/MobileDevice/(your device name)
Windows XP: C:\Documents and Settings\(your username)\Application Data\Apple Computer\Logs\CrashReporter\MobileDevice\(your device name)
Windows Vista / 7: C:\Users\(your username)\AppData\Roaming\Apple Computer\Logs\CrashReporter\MobileDevice\(your device name)
and locate the appropriate log file or files (should have names starting with "Pleco" and the file extension .crash). Send those files to
mikelove@pleco.com and we'll get to work on them.