Issue #1506: Post-compile enhancement sometimes causes error in generic loops: incompatible types found: java.lang.Object: required: Entity

I have moved from automatic run-time enhancement to explicit post-compile enhancement in an Ant build.xml in a NetBeans web app, and sometimes on editing a file that performs a generic for loop over an @entity type I get a generics error. The generic for loop is: 

for (Steel s: this.steelMaterials.getL_Steel().getEls()) {
 ..
}

Where getEls() here gives:

List<Steel>

This sometimes (only, I don't understand the circumstances) gives this error:

incompatible types
found: java.lang.Object
required: com.example.entity.Steel
        for (Steel s: this.steelMaterials.getL_Steel().getEls()) {

The workaround is to simply clean and build the entire project, which is quite tedious and time-consuming.

I appreciate any feedback on how to address this to improve my development cycle, which is compromised by this.

This rewrite of the generic for loop works but it is inconvenient to have to remove generic loops just because of enhancement:

for (Object os : steelMaterials.getL_Steel().getEls()) {
 if (os instanceof Steel) {
  Steel s = (Steel)os;
  // do something with "cast" Steel (no pun intended)
 }
}

Could you please provide a simple console test case that demonstrates this issue?