TestFieldCacheSanityChecker.testInsanity1 failure [LUCENE-4646]

I've hit this while running tests:

```
[junit4:junit4] Suite: org.apache.lucene.util.TestFieldCacheSanityChecker
[junit4:junit4] 2> NOTE: reproduce with: ant test -Dtestcase=TestFieldCacheSanityChecker -Dtests.method=testInsanity1 -Dtests.seed=7E0EF33CC742369A -Dtests.slow=true -Dtests.locale=sr_RS_Latn -Dtests.timezone=ECT -Dtests.file.encoding=UTF-8
[junit4:junit4] FAILURE 1.30s J0 | TestFieldCacheSanityChecker.testInsanity1 <<<
[junit4:junit4] > Throwable #1: java.lang.AssertionError: wrong number of entries in cache error expected:<2> but was:<4>
[junit4:junit4] > at __randomizedtesting.SeedInfo.seed([7E0EF33CC742369A:15B02AB0AB1CB68A]:0)
[junit4:junit4] > at org.junit.Assert.fail(Assert.java:93)
[junit4:junit4] > at org.junit.Assert.failNotEquals(Assert.java:647)
[junit4:junit4] > at org.junit.Assert.assertEquals(Assert.java:128)
[junit4:junit4] > at org.junit.Assert.assertEquals(Assert.java:472)
[junit4:junit4] > at org.apache.lucene.util.TestFieldCacheSanityChecker.testInsanity1(TestFieldCacheSanityChecker.java:135)
```

Failed to reproduce with the seed w/ and w/o tests.method. Tried w/ tetss.iters=100, but did not reproduce either.

---
Migrated from [LUCENE-4646](https://issues.apache.org/jira/browse/LUCENE-4646) by Shai Erera (@shaie), updated Jan 31 2013
Linked issues:
- #5802

Start with org.apache.lucene.util.TestFieldCacheSanityChecker.testInsanity1 and the assertion at TestFieldCacheSanityChecker.java:135. Run the provided ant test command with the recorded seed, then investigate why the cache entry count is expected to be 2 but observed as 4; done means the intermittent failure has an identified cause and a verified resolution.

Written by the indexing model from the issue text.