Thanks for the bug reports Numbers! Indeed all things look like bugs. Regarding bug 3 I suppose it has to do with the inventory's capacity. If the inventory is nearly full, runics created won't get added to it; without warning the player.. doh not very nice. Regarding bug 1, the fix should be easy.
Onto bug 4, I suppose it has to do with the version of java shipped with Dungeon Mercenary. Dungeon Mercenary's desktop version embeds a Java 8 virtual machine, but Java 8 is now circa 5 years old and your system may refuse running it. Can you tell me your operating system details? A very-likely-to-work solution would be to install Java 8 on your system and launch Dungeon Mercenary using the file named dm-18-04-30.jar in the downloads (which is flagged Linux but can actually work on all three OSes) by executing java -jar dm-18-04-30.jar in Windows' terminal.