ADDITIONAL SYSTEM INFORMATION :
> uname -a
Linux XXX 6.5.0-18-generic #18~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Feb 7 11:40:03 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

> java --version
openjdk 21.0.2 2024-01-16
OpenJDK Runtime Environment (build 21.0.2+13-Ubuntu-122.04.1)
OpenJDK 64-Bit Server VM (build 21.0.2+13-Ubuntu-122.04.1, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
Parsing of the year is unexpected if there is optional fields in the pattern e.g. "uuuu[MM]". This pattern cannot parse input: "200001". It fails on parsing the year part. Somehow year parsing tries to greedily parse the whole input and fails.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
jshell> import java.time.format.DateTimeFormatterBuilder;
jshell> (new DateTimeFormatterBuilder()).appendPattern("uuuu[MM]").toFormatter().parse("200001");


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
{MonthOfYear=1, Year=2000},ISO
ACTUAL -
| Exception java.time.format.DateTimeParseException: Text '200001' could not be parsed at index 0
| at DateTimeFormatter.parseResolved0 (DateTimeFormatter.java:2108)
| at DateTimeFormatter.parse (DateTimeFormatter.java:1936)
| at (#43:1)

---------- BEGIN SOURCE ----------
jshell> import java.time.format.DateTimeFormatterBuilder;
jshell> (new DateTimeFormatterBuilder()).appendPattern("uuuu[MM]").toFormatter().parse("200001");
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
jshell> (new DateTimeFormatterBuilder()).appendValue(ChronoField.YEAR, 4, 4, SignStyle.EXCEEDS_PAD).appendPattern("[MM]").toFormatter().parse("200001");
$47 ==> {MonthOfYear=1, Year=2000},ISO

FREQUENCY : always