Oblique projection (Ob): Partly wrong annotations

**Description of the problem**

_Related to this forum post https://forum.generic-mapping-tools.org/t/how-to-set-the-annotation-of-x-axis-as-latitude-when-i-use-oblique-projection/4751/13_

Here, I try to summarize the main findings so far.:
* Overall there is an issue with the annotations for the Oblique projection **Ob**. Partly the West-East and South-North directions are mixed up.
* The issue does not occur in GMT 6.1.0 (please see https://forum.generic-mapping-tools.org/t/how-to-set-the-annotation-of-x-axis-as-latitude-when-i-use-oblique-projection/4751/7?u=yvonnefroehlich).
* Explicitly setting `--MAP_ANNOT_OBLIQUE=anywhere` can help to fix the issue in some cases. However, the documentation states that this is the default (please see https://docs.generic-mapping-tools.org/dev/gmt.conf.html#term-MAP_ANNOT_OBLIQUE).
* Appending / not appending **+v** to **-J** has an effect whether the issue occurs.

**Full script that generated the error**

_Case I (GMT forum)_
Top Left
```
gmt grdimage @earth_relief -JOb168/51/172/32.5/6c -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 -png lon_lat
```
Top Right
```
gmt grdimage @earth_relief -JOb168/51/172/32.5/6c+v -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 -png lon_lat_v
```
Bottom Left
```
gmt grdimage @earth_relief -JOb168/51/172/32.5/6c -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere
```
Bottom Right
```
gmt grdimage @earth_relief -JOb168/51/172/32.5/6c+v -R-500/2300/-400/400+uk -Ggray -BeNsW -Bxa5f1 -Bya5f1 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere_v
```

| Top Left: Wrong | Top Right: Correct |
| --- | --- |
|  |  |

| Bottom Left | Bottom Right |
| --- | --- |
|  |  |

_Case II (PyGMT docs)_
Top Left
```
gmt coast -JOb130/35/25/35/6c -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 -png lon_lat_02
```
Top Right
```
gmt coast -JOb130/35/25/35/6c+v -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 -png lon_lat_v_02
```
Bottom Left
```
gmt coast -JOb130/35/25/35/6c -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_anywhere_02
```
Bottom Right
```
gmt coast -JOb130/35/25/35/6c+v -R130/35/145/40+r -Ggray -BWSNE -Bxa5f1g5 -Bya2f1g2 --MAP_ANNOT_OBLIQUE=anywhere -png lon_lat_v_anywhere_02
```

| Top Left: Correct | Top Right: Wrong |
| --- | --- |
|  |  |

| Bottom Left | Bottom Right |
| --- | --- |
|  |  |

**Full error message**

No error message occurs.

**System information**

* Operating system: Windows and Linux
* GMT version (`gmt --version`): GMT 6.5